Technology
PRE-OXIDATION.
Why it is necessary
Some polluting substances exist in water in reduced form that makes it difficult to remove them. The purpose of pre-oxidation is to convert such substances to oxidised form to facilitate their removal.
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How to do it
With addition of oxidizer. It can be potassium permanganate or sodium hypochlorite or any chemical permitted for use for potable water purification. Pre-oxidation generally has a disinfecting effect too.
COAGULATION FLOCCULATION.
Why it is necessary
A certain share of polluting substances in water cannot be filtered. During coagulation these substances are converted to solid status, then filtered out of water.
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How to do it
With addition of coagulants. These are generally iron or aluminium salts. After the addition of chemical the water is kept for a short time in a container designed for this purpose - a flocculator - to allow sufficient time for the chemical to enclose the polluting substances in floccules that can well be filtered.
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Is addition of chemicals dangerous
No. The chemicals applied have been used for many decades in water purification plants worldwide. With appropriate dosage these too will entirely be removed during filtering.
PRE-FILTRATION.
Why it is necessary
Larger solid particles in the water to be treated must be removed from the water since these are not desirable in potable water either, and finer filtration units could quickly be blocked and damaged by larger particles.
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How to do it
With micro-filters. These are filters with 100-400 μm pore size, depending on the type selected. Particles with a larger size are simple caught in the filter like in a noodle sieve or mosquito-net. It is, however, important that each of the filters used in our equipment automatically cleans itself when too much pollution has been accumulated in it.
ULTRA-FILTRATION.
Why it is necessary
This way the polluting substances – converted to solid form – can be removed from the water. Ultrafiltration makes the water clean.
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What is ultrafiltration?
This is a modern filtration technology using membranes with which solid pollutants are filtered out of water. Ultrafilters have a nominal pore size of about 0.02-0.04 μm. This extremely small size enables such fine filtration that enables filtering out of water 99.9% of bacteria and even a certain share of viruses. This means that it is very safe.
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Are there any disadvantages to ultrafiltration?
Yes, there are. It is more expensive than conventional sand filtration, in exchange it is much more efficient and safer. It needs to be flushed, cleaned more frequently, thus water loss is higher, and automation with appropriate standard is important.
Why ultrafiltration
Because it is extremely efficient and safe. The quality of ultrafiltered water is excellent, currently it is the best filtration technology available.
POST-DISINFECTION.
Why it is necessary
The raw water to be treated may contain – particularly surface water – pathogenetic micro-organisms that need to be removed or destroyed to make consumption of water safe.
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How to do it
Basically, ultrafiltration technology removes more than 99% of potential pathogens, but for safety reasons, we also add a chlorine-based disinfectant (sodium hypochlorite) to the treated water. This also kills most of the remaining microorganisms and leaves a small amount in the water so the water stays safe to consume.
CIP - CLEANING IN PLACE.
What is CIP
CIP means cleaning with chemicals the CIP ultrafilter membranes. During filtration sooner or later deposits (e.g. boiler scale) accumulate on the surface of the membranes that cannot be removed by regular backwash. Consequently, the permeability of the membranes reduces, thus the capacity of the equipment also decreases. During cleaning with chemicals these deposits are removed to restore the good condition of the membranes.
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How to do it
The equipment is stopped. The appropriate washing solution is prepared in a container used for this purpose, then it is conducted to and circulated through the membranes. After the relevant action time has elapsed the washing solution is pumped off the membranes and the membranes are flushed with clean water. During the period of cleaning water production is suspended. The period of washing depends on the pollution level of the membranes, can take 2 to 8 hours, can be required, depending on the quality of water, every 1 to 6 weeks.
Is cleaning with chemicals dangerous
During cleaning with membranes the chemicals cannot get to potable water, therefore it is not dangerous. The chemicals used (acids, alkali) are hazardous themselves, but if basic labour safety regulations are followed, use of these chemicals does not pose any major risk.
Process Flow Diagram
+ About Reverse Osmosis (RO).
What is reverse osmosis
It is a procedure using semipermeable membranes that water molecules can penetrate, but larger molecules cannot. This procedure removes to a close approximation everything from water, including substances existing in solutions that cannot be removed by filtration. It is to such extent efficient that minerals removed during the purification need to be added to water again to make it fit for human consumption. It can be used also for desalination of seawater, depending on the type of membrane used, although the RO device offered by us can only be used for treating fresh water and brackish water.
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What are the disadvantages of RO
It is an expensive technology in terms of both investment and operation costs (although when it is needed, high costs are relative). The water loss with this technology is significant, for fresh water it can be 25-30%, for seawater even up to 60%. The treated water is “excessively clean”, therefore salt needs to be added again to make it fit for consumption that requires significant quantity of salt to be supplied.
When reverse osmosis needs to be used
When polluting substances in solution exist in water which cannot be converted to solid form (that can be filtered), but need to be removed. Another case is when potable water needs to be produced from water with unknown quality, and appropriate laboratory background is not available for checking the quality of the treated water. This can occur in disaster situations.